This research project consists of biomechanical investigations of the function of the human larynx in phonation. Specific aims are (1) to quantify the mechanical stress pattern in the vocal folds for specific modes of vibration, (2) to measure the biomechanical properties (viscoelastic and vibrational) of larynx tissues examined molecularly in Project R2, (3) to discover the optimum synthetic materials and geometry of a mechanical model of the vocal fold mucosa, (4) to quantify the effects of asymmetry of the vocal folds, using methods of nonlinear dynamics, (5) to develop an index of vocal efficiency (or economy) that includes tissue collision and internal mechanical stress as a cost factor. Together, the studies constitute an investigation of the physical and biomechanic properties of the major sound source in speech production. The outcome of the studies will have direct impact on diagnosis and treatment of voice disorders. In particular, the direct tie to the molecular investigations by Dr. Gray in Project R2 will lay the groundwork for understanding the etiology of benign vocal lesions, such as nodules, polyps, contact ulcers, and granulomas. Experimental procedures include the use of excised human and animal tissue as well as human subjects. The bulk of the parametric experimentation, however, is done on physical and computer simulation models. In particular, a finite-element simulation model of vocal fold vibration is used to integrate fragmentary pieces of information obtained in isolated experiments. This allows for a high degree of theoretical interpretability of the data obtained from isolated tissue and human subjects.